findFontSizeDecl.js

function findFontSizeDecl(root) {
  var vals = [];

  // Iterate over font-size declarations
  root.walkDecls(/font-size/, function(decl) {
    vals.push(convertToEm(decl.value));
  });

  return vals;
};

var ROOT_FONT_SIZE = 16;
function convertToEm(value) {
  if (value == 0) return 0;
  if (value.indexOf('rem') > 0) {
    return parseFloat(value.slice(0, -3));
  }
  if (value.indexOf('em') > 0) {
    return parseFloat(value.slice(0, -2));
  }
  if (value.indexOf('px') > 0) {
    var pixels = parseFloat(value.slice(0, -2));
    return pixels/ROOT_FONT_SIZE;
  }
  // Skip declarations of inherits, initial
  console.log('Skipping: ', value);
}